1. Field of the Invention
The present invention relates to a connector assembly for connecting an optical fiber cable to a socket.
2. Description of the Related Art
It is known in the field of optical communications to terminate an optical fiber transmission cable by ending the optical fiber in a connector, with the optical fiber secured in a ferrule. Such a connector is used to connect the optical fiber cable, through a socket, to other devices, such as sources, detectors or repeaters, or to passive devices like switches or attenuators.
Typically, a connector is assembled by first taking one end of the optical fiber cable and stripping off the protective covering, exposing the bare optical fiber, which is usually about 125 .mu.m in diameter. Next, the fiber is inserted into a hole in the center of a ferrule, which may be a plug-type, a biconic type, or other type, so that the end of the optical fiber extends a short distance from the end of the ferrule. The optical fiber is then secured to the ferrule by epoxy, glue, adhesive or any other means, and the end is polished flush with the end of the ferrule.
A housing is placed around the ferrule and the optical fiber to hold the ferrule and to provide strain relief for the optical fiber. The actual design of the housing depends on the intended use for the connector. The optical fiber is very fragile and can be broken quite easily. The housing typically clamps to a protective cable around the optical fiber and holds the ferrule so no stress is applied directly to the optical fiber itself.
A typical example of an optical fiber connector assembly employing an ST.RTM. connector and which includes a glass ferrule is disclosed in U.S. Pat. No. 4,934,785 to Mathis et al. Another example of an optical fiber connector is disclosed in U.S. Pat. No. 4,834,487 to Abendschein et al., which describes an optical connector assembly which includes a plastic alignment ferrule. In these patents, the end of the optical fiber cable is inserted in the ferrule and the end of the ferrule is polished in the field where the connector assembly is needed.
A problem associated with such known connectors arises in centering the fiber in the ferrule and in centering the ferrule in the receptacle. If the optical fiber is not exactly centered in the ferrule, and if the ferrule cannot be exactly centered in the receptacle, a loss of light energy will occur due to misalignment. Hence, tight tolerances are needed to maintain the diameter of the hole in the ferrule, the location of the hole and the centering of the optical fiber in the hole while it is secured in the ferrule.
In order to maintain proper positioning of a fiber optic cable during assembly of a fiber optic connector, it is not always possible to maintain these tight tolerances without extensive equipment and time. This limitation becomes more important for single mode fibers whose core diameters are on the order of 9 .mu.m, where even tighter tolerances must be maintained. For example, the optical fibers must be located to within.+-.0.75 .mu.m of the optical axis, which is determined by the socket, to insure losses less than 0.1 db for a connector for the single mode fibers. The optical fiber diameter tolerances are typically .+-.1 .mu.m, and the concentricity of the core is typically .+-.0.5 .mu.m. Hence, the eccentricity of the core of a fiber in a ferrule which is just large enough to accept the largest fiber could be as much as 1.5 .mu.m. Any additional error in the ferrule hole concentricity or diameter could increase the eccentricity of the fiber mounted in the ferrule. The quality of the polishing of the end of the fiber can also markedly effect fiber coupling losses.
While techniques have been developed to improve this task in the laboratory or in a manufacturing facility, installment in the field of a connector many times results in connectors with high light energy losses. These energy losses thus result in the need to re-make the connector, which in turn results in wasted connectors and lost time. Thus, a need exists for a reliable connector assembly which can be assembled in the field with minimum energy loss.